city bird

I’ve been learning a lot about birds this year, and my new favorite thing about spring has been recognizing the robin songs I hear early in the morning every day. Bird song is the only evidence of wildlife most students will experience in a day at the University of Cincinnati. In a dense urban environment like this, animals are much better heard than seen.

We don’t hear bird song over the hum of cars and AC units by accident – songbirds naturally sing louder in the presence of environmental noise. In particular, humans clog the airwaves with low-frequency sounds that push bird songs to be higher in pitch. For humans, this means we get to engage with wildlife even in our noise polluted cities. For birds, the consequences of adapting to human noise can cost lives.

Songbirds adapting their calls to the soundscape of their habitat is nothing new. These animals have the most complicated vocal structure on the planet (the syrinx, as opposed to our larynx) and will tune their vocalizations to the frequencies that work best for their environment. 

Considering how fantastic their voice boxes are, their ears are pretty terrible. Birds don’t have the external ears that help humans and other animals focus and localize high frequency sounds. Songbirds also have really small heads – about as wide as your thumb. This means it’s more difficult to triangulate where sounds are coming from because their ears are so close together.

Of course, their “primitive” ears also seem to be immune to aging and are a true medical phenomenon, a testament to how important hearing is to songbirds. Despite their immortal ears, though, songbirds have a hearing range that is much lower and smaller than humans. Altogether, birds can only hear and localize frequencies from about 10-10,000 Hz, compared to 20-20,000 Hz for humans. They also have a higher threshold for hearing, so they need to get closer than humans to things like airplanes and wind turbines before they can hear them.

In particular, birds hear best between 1 and 4 kHz, coincidentally similar to humans, which is why we love their songs so much. How low a male songbird can sing is a big part of its mating potential, and some species like pigeons can sing much lower than humans can even hear. While singing low is great for passing on your genes, its impossible to project these frequencies above the low noise that humans create.

Human noise pollution has brought urban reproductivity rates down in songbirds, and the higher frequencies that birds must reach can strain their bodies and damage their voice boxes. Some urban bird songs have even become unintelligible to their country counterparts, flattening the gene pool and further fracturing wildlife populations.

Too much noise is just one of the many ways that our human habits hurt songbirds, and if we want to keep our last city wildlife around we may need to quiet down. Reducing sounds from highways, packed stadiums, and constant construction are just a few of the ways we can reduce noise pollution in our city.